Disowning children: Why Would Parents Do That?

Children are supposed to bring joy to the parents but to some parents, their expectations and their disrespect for their children cause relationship problems. Some even resort to disowning their children. A good example is when their children refuse to marry a person of their choice, or of the same religion. The first thing that pops into the parents' mind is to disown them to show that they mean business. This should never happen, why do parents think of disowning their own flesh and blood?
What's your opinion on this?